When two things react the one with the more negative (if they're both positive this means closest to 0) electrode potential will be the on that goes backwards and the other one will go forwards.
This means that if you want to oxidise chromium(II) to chromium(III) you want that reaction to go backwards so you want something less negative than -0.41.
In case you hadn't realised, the oxidation state of the chromium in (Cr2O7)2- is chromium(VI) and based on the questions you don't want this reaction to go backwards so you want something more negative than +1.33.
This means that you want something from the table with an electrode potential between -0.41 and +1.33 so the answer is iodine and bromine.
I'm very sorry if this is incorrect, I only wrapped my head around this topic myself very recently.

(Original post by LaM19)
When two things react the one with the more negative (if they're both positive this means closest to 0) electrode potential will be the on that goes backwards and the other one will go forwards.
This means that if you want to oxidise chromium(II) to chromium(III) you want that reaction to go backwards so you want something less negative than -0.41.
In case you hadn't realised, the oxidation state of the chromium in (Cr2O7)2- is chromium(VI) and based on the questions you don't want this reaction to go backwards so you want something more negative than +1.33.
This means that you want something from the table with an electrode potential between -0.41 and +1.33 so the answer is iodine and bromine.
I'm very sorry if this is incorrect, I only wrapped my head around this topic myself very recently.